Put all ingredients into a saucepan (no need to fry up the onion first, we want the juice of the onion to be part of the sauce), bring to a boil and simmer ​for one hour. Stir occasionally.

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Put all ingredients into a saucepan (no need to fry up the onion first, we want the juice of the onion to be part of the sauce), bring to a boil and simmer ​half an hour. Put through a blender, and boil down until the consistency is right (another half hour with the lid removed).